When a microwave system propagates a signal in free space, propagation of the signal is affected by free space attenuation, rain attenuation, atmospheric absorption, multipath attenuation, and the like. Under normal conditions, only normal attenuation, such as the free space attenuation and the atmospheric absorption attenuation, occurs. In this case, a power of a signal that reaches a receiver is far greater than a receiver sensitivity power (a sensitivity power is defined as a minimum receive power that ensures normal transmission of a signal, and receive power that results in a system bit error rate of 1E−6 is usually used to weigh sensitivity), and the system can work normally. Under adverse weather conditions, abnormal attenuation, such as the rain attenuation and the multipath attenuation, occurs at the same time, and the receive power decreases significantly. When the receive power decreases below the receiver sensitivity power, the system cannot properly transmit the signal, and the system enters an unavailable state. In order to reduce total unavailable time of the system as much as possible, a link planner of the microwave system generally designs a normal receive power to be far greater than the sensitivity power, and a part of the normal receive power in excess of the sensitivity power is referred to as fade margin, which is used to resist abnormal attenuation such as the rain attenuation and the multipath attenuation under adverse conditions.
The sensitivity power of the microwave system mainly depends on performance of the system itself, but when the microwave system is affected by interference from a signal that operates at a same frequency and is from another receiver, sensitivity of the microwave system deteriorates. At this time, effective fade margin of the microwave system reduces, and the overall availability decreases. Therefore, a microwave network planner expects to know whether a current microwave link is affected by co-channel interference, and assesses whether the interference is within an acceptable range.
In prior art 1, a transmitter transmits a signal with an operating frequency of the transmitter, while a receiver receives a signal with a same frequency; the transmitter that is working is set to off, so that the transmitter stops transmitting any signal; at this time, the receiver detects a power of the received signal with the operating frequency, and if the power is detected, it is considered that the detected power is a power of a signal from another receiver, that is, co-channel interference power. Low power interference cannot be detected by using this method. Due to the reason of costs, a minimum receive power that can be detected by a receiver of the microwave system is around −90 dBm (Decibel Referenced to one milliwatt, dBm), and detection of a lower power will lead to a significant increase in costs. Therefore, a minimum interference power that can be measured in the above technical solution can only be around −90 dBm. However, an interference detection capability of −90 dBm is often insufficient, as co-channel interference less than −90 dBm also leads to significant sensitivity deterioration of the microwave system.
Meanwhile, in prior art 2, a transmitter transmits a signal with an operating frequency of the transmitter, while a receiver receives a signal with a same frequency; the operating transmitter gradually decreases its transmit power, and a receive power of the receiver also decreases at the same time. At the same time, the system gradually produces a bit error. When a bit error rate of the receiver reaches 1E−6, the receive power is equal to an actual sensitivity power at this time. Whether frequency interference exists at this time may be learned by determining whether the sensitivity power deteriorates at the time. In addition, an interference power value can be calculated according to an extent of sensitivity deterioration. The transmitter in the method requires a relatively large transmit power adjustment range, for example, an adjustment range greater than 40 dB (Decibel, dB), so that the receive power of the receiver can decrease to a level of the sensitivity power by adjusting the transmit power of the transmitter. However, costs for implementing a power adjustment range of 40 dB for a transmitter are relatively high; in addition, according to the method, whether the receive power reaches the receiver sensitivity is determined by observing the bit error rate of the system. Because observation of the bit error rate is a time-consuming process, measurement time in prior art 2 is relatively long.